Prior art panoramic dental X-ray machines are well known. Some provide a continuous image of the dental arch area and commonly employ an X-ray source and X-ray film both optically aligned with each other and supported on a rotatable carrying arm which orbits a patient situated in the path of the X-ray beams. The patient may remain stationary or be transported in a patient chair in accordance with various type drive mechanisms in order to simulate the generally elliptical shape of the human dental arch. The continuous image radiograph provides the dentist with a panoramic view of the teeth and associated structures and is therefore a useful diagnostic aid in many phases of dental practice.
Various other prior art apparatus provide a discontinuous, or split image panoramic radiograph which possesses certain advantages. Here, the dentist is presented with additional interpretive information since two distinctly different views of the incisors, or centrals area are provided. Additionally, overlying spinal shadow which would be cast over the central-bicuspid region are eliminated since X-rays are not generated when the spine is aligned with the X-ray source and film.
Regardless of the type radiographic image to be obtained, i.e., continuous or discontinuous, compensation is usually made for the fact that the curvature of the desired area of focus is generally not a true circle or ellipse. Thus, the rate of film travel must be varied in accordance with the rate of travel of the X-ray source about the patient's head in order that the radiological projections occupy a distance on the film equal to the linear distance of a curved structure being X-rayed, such as a typical dental arch.
In U.S. Pat. No. 2,798,958, apparatus is disclosed for varying the rate of film travel relative to the rate of travel of the X-ray source. The X-ray source and film carrier are both supported by a single member permitting both the X-ray source and film carrier to orbit the patient at an uniform rate of travel. Means are also disclosed for reorienting the patient after completion of one-half of the excursion cycle in order to relocate the center of the axis of rotation with respect to the patient's head prior to X-raying the other one-half of the dental arch in order to provide the discontinuous, or split radiographic images.
In U.S. Pat. No. 3,045,118, apparatus is disclosed which automatically shifts the patient in order that the line of sight between the X-ray source and film bypasses the patient's spinal column and permits X-raying of the other half of the dental arch. Apparatus is also disclosed therein for continuously moving an X-ray source and extraoral film holder about the patient.
In U.S. Pat. No. 3,636,349, structure is disclosed for revolving the X-ray source and film carrier about the head of a patient who remains fixed in position while the centerline of the orbit continuously moves through an arcuate path approximating the arch of the patient's teeth. The patent further discloses film carrier means which may be used advantageously in the practice of the present invention.
Thus, the prior art discloses various types of structures, apparatus and mechanisms for orbiting the X-ray source-X-ray film (tube-head-camera) assemblies in circular or arcuate paths; for varying film travel speed in accordance with tubehead-camera assembly movements; for shifting the patient in a chair; and for providing continuous or discontinuous type radiographic images.
In each of the aforedescribed prior art systems, the patient is subjected to radiation doses of sufficiently high intensity in order to project the desired images adequately onto the X-ray film. The presence of a large X-ray tubehead was necessary, including means to power and control it. Further, the chair carrying the patient was often-times shifted at an appropriate moment in order to bypass the spinal column; and/or the tubehead-camera assembly was caused to describe an arcuate path in an attempt to duplicate the shape of a typical dental arch.
The present invention will be described hereinafter substantially in conjunction with an intraoral radioactive point source, but it is intended to embrace intraoral X-ray sources as well.
The present invention eliminates the need for (a) X-ray tubehead and means to power and control it, (b) chair shift, and (c) non-circular path of the camera assembly. An intraoral radioactive point source is herein provided which coacts with a circularly orbiting camera assembly such that radiation emanating from the radiation point source and passing through the patient's dental arch structures is automatically continuously collimated with a slit diaphragm, or slot, disposed in a central forward portion of the camera assembly. The radioactive point source is enclosed within a shielded container having an axis of rotation which is not a fixed point within the patient's mouth, but where the axis of rotation is continuously moved along a predetermined horizontal arc within the mouth to thus provide undistorted images of dental arch structures. The radiation entering the camera slot may then be received by an image intensifying device secured within the camera assembly, and the output from the image intensifier activates light-sensitive film for producing the full size panoramic radiograph. In lieu of, or addition to the radiograph, an electronic display of the images may readily be obtained if desired.
The present invention does not require the presence of an image intensifying device. That is, conventional X-ray film with intensifying screens may be used advantageously wherein the intraoral X-ray source may be a rod anode which is conveniently disposed in an X-ray transparent wedge-shaped bite block, for example.
Additional advantages, among others, to be derived from practicing the present invention are reduced radiation dosage to the patient and sharper images on the radiograph due to an absence of interfering structures between the radiation source and dental arch compared to extraoral source systems. By controllably moving the radiation source within the mouth of the patient along a predetermined horizontal arc, described later, a more favorable geometry of source-to-patient-to-camera is realized for decreasing overlap of adjacent teeth to provide more valuable diagnostic information, for example, of caries between adjacent teeth. Further, small segments of the dental arch may be scanned to efficiently perform periapical and bite-wing functions with different geometry and magnifications. Still further, radiographing of the entire dental arch structure with only a single scan may be achieved, as opposed to known prior art methods which require two separate views of the dental arch, each view or scan being made from a different fixed point and where the film is stationary. It is understood, of course, that two or more scans may be utilized as an alternative.